After the strong earthquake in Pakistan a good part of the media coverage was about the fascinating story of the new island that emerged off Gwadar. While this was really amazing I think now it’s time to think about the consequences of the quake itself. We have seen a shallow M7.7 event that produced severe shaking across a large area. Peak ground acceleration exceeded 1 g in the 0.3 s period and was still intense in longer periods. 515 people have reportedly been killed and more than 100,000 are homeless. The huge number of destroyed houses is easily explained by two facts:
- The very strong shaking and
- The traditional buildings.
This photo series of Boston.com tells the entire story. Especially images 1, 8, 9, 16-19, 21, and 22 are interesting from an earthquake engineering point of view. Traditional houses are made up of mud bricks and partly also supported by large rounded rocks that are used for the walls. This construction type has several advantages:
- It’s cheap;
- It can be built almost everywhere;
- No wood is needed, which is rare in this area and better used for heating;
- It’s relatively easy to build and repair a house and
- It keeps the house cool during the summer heat.
Obviously, the big disadvantage is:
- It will kill you during an earthquake.
Even smaller quakes can cause this type of structures to collapse. This is what happened in Bam, Iran, in 2003. So now we see that people rebuild their houses in the same way they were constructed before, and we know that significant aftershocks might last for months (one aftershock of magnitude M6.8 already killed 22 people). Of course, due to the lack of money, international help and alternatives there is no other option for the locals. They must re-built their houses as soon as possible. But we all know that it’s not really a good idea. People should be taught on how to build simple, more earthquake resilient houses and they should be given the building material for free now. It’s clear that in the epicentral area of a shallow M7.7 quake even rather stable structures would face problems, but with our technological knowledge there is no need to see thousands of houses being destroyed.
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